In response to recent social demands and trends in the context of energy and environment problems, fuel cells capable of operating even at ordinary temperature and obtaining high output density have attracted attention as a power supply for an electric car and a stationary power supply. A fuel cell is a clean power generation system in which an electrode reaction product is water in principle and which reduces the load on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power supply for an electric car because it operates at relatively low temperature.
A membrane electrode assembly (MEA, hereinafter also referred to as MEA) included in a single cell of a fuel cell includes an electrolyte membrane where a catalyst layer is disposed, and frame-shaped gaskets disposed on opposite surfaces of the electrolyte membrane. The gaskets are positioned to surround the catalyst layer of the electrolyte membrane, and have the function of preventing fuel gas and oxidant gas supplied to the catalyst layer from leaking outside.
As a technique of suppressing remaining of bubbles between a plurality of sheet members when stacking (bonding) the sheet members, a resin sheet having through holes is known (see, for example, International Publication No. WO 2004/061032).
Even if the resin sheet of International Publication No. WO 2004/061032 is applied to the gaskets in the MEA, there is an area where bubbles cannot be removed by the through holes, and it is difficult to suppress remaining of the bubbles.
Owing to the remaining bubbles, the area surrounded by the gaskets sometimes communicates with the outside of the gaskets. Alternatively, projections are sometimes formed in the gaskets by the remaining bubbles, and the projections reduce the adhesion between the gaskets and separators. These may cause fuel gas and oxidant gas supplied to the catalyst layer to leak outside.